Have you checked the character map for the web font you use in your WordPress theme?
Thanks to all web fonts, nowadays we have much more choices for fonts in our WordPress themes. You might have checked if your theme looks good with Lorem Ipusum text but I’m afraid that’s not good enough. Lorem Ipusum text doesn’t have all digits, punctuations, and symbols from the Basic Latin character set. A WordPress theme should support at least all the Basic Latin characters, and this is only assuming your theme will be used for English language. This seems to be basic but often it’s overlooked.
Here is an example.
This is the character map of the popular free font ChunkFive.
Similar looking font, Beval‘s character map.
If you want to support other languages, Spanish for example, you need to check the Latin-1 Supplement too. I’m not going to be able to give you all examples in here but you get the idea. Don’t forget to check the character map before you decide the web font you use in your WordPress theme.
*Both character maps are taken from FontSquirrel.com (Feb 26th, 2010)